In recent years, a light emitting device using a self-luminous element has been advanced in research and development and drawing a great deal of attention as a next generation display. This self-luminous element has an element structure that a layer containing an organic compound is sandwiched between an anode and a cathode.
One of driving methods in the case of displaying a multi gray scale image with a light emitting device using a self-luminous element is a current input method. In this current input method, current value data is written to a self-luminous element as a signal to control luminance. The luminance is in proportion to a current supplied to the self-luminous element (hereinafter simply referred to as a signal current), therefore, the signal current is required to be accurately supplied to the self-luminous element. However, as the characteristics of active elements (specifically transistors) configuring a power supply for supplying a signal current vary, it is difficult to input an accurate signal current to the self-luminous element.
To solve a problem that the luminance non-uniformity due to variations in characteristics of thin film transistors (TFTs) and OLEDs in a driving method of current input, a configuration has been suggested in which a current specification type AM drive pixel circuit using a polysilicon transistor and a DAC circuit having a reset function are provided to OLED as a driving method by the current input method. It is also disclosed that a channel length is designed long, and the like.